The invention relates to a device for the generation of a control voltage across a piezo-electric positioning element, in particular for positioning a recording and/or reproducing element relative to an information track.
There are numerous systems employing a piezo-electric positioning element, for example for positioning recording and/or reproducing elements in magnetic or optical recorders, both with record carriers in the form of a tape and a disk, in order to ensure that the element correctly follows the information track (for example in video cassette recorders), or for controlling the position of the element relative to the information track (azimuth control in audio cassette recorders).
Such a system is for example known from German Pat. Application No. 27 11 935 which has been laid open for public inspection, an analog control voltage being applied to a piezo-electric element via a voltage amplifier. Piezo-electric elements are controlled with a comparatively high voltage, so that such a voltage amplifier requires a comparatively high supply voltage, which in the example of the said German Patent Application is a symmetrical supply voltage of +200 V and -200 V. This in itself is a disadvantage because the other components of an apparatus comprising such an amplifier operate with a comparatively low supply voltage, so that this high voltage must be generated separately for said voltage amplifier, which is particularly inconvenient in the case of battery-powered equipment because of the required d.c. transformation and the comparatively high dissipation of such a voltage amplifier.
The applicant's U.S. Patent Application Ser. No. 41,673 (PHN 9136) filed May 23, 1979, describes a system for controlling the position of a read head relative to a record carrier in the form of a tape, which system generates pulse-shaped control signals. When a voltage amplifier is used for applying a control voltage across the piezo electric element, this signal would first have to be converted into an analog voltage, for example by integration,